Here's most of what I've learned so far.
The Gathering Foot:Amazon price tag is for real! I had two friends order it last week! I set my stitch length to 5 - or the longest it will go, for the tightest gather. And then I run my fabric or crepe paper or whatever right underneath the very bottom of the foot.
I've also occasionally used it to gather something as I sew it to another piece of fabric. It's a little bit tricky, and definitely requires some practice, but you can do it if you place the fabric to be ruffled under the bottom of the foot, and the other fabric in the little slot that you see that opens to the left. You have to be very careful not to pull on the "ruffle" fabric as you sew though or else it won't gather consistently.
The Ruffler Foot:Amazon. Be sure to shop around! It's a lot scarier looking, but itt's amazing to watch it work. My ruffling foot says it can be adjusted to make repeating tucks, narrow pleats, smocking and shirring. But since the instructions are teensy tiny, I haven't taken the time to figure out all the cool things that it can do yet. It has a little lever/switch that you can use to change up the pleats to varying sizes.
The Recap:So basically, one pleats, and one gathers. The gathering foot is super fast for me to put on, so I do have a tendency to favor it. I'm always in a hurry to ruffle something. And I get impatient. But I do have big plans for some pillows or pretty garlands smothered in yards and yards of pleated ribbon. Be sure to let me know if you end up getting one and using it on projects! I'd love to see photos or links!